Yes, a dedicated database service for this could make sense to separate writes if tracking changes starts taking most of the database writes. I suggested this as a means to offload some of the load if it starts to become a problem- but I do not know what are the needs in terms of joins and all, so this would be a nice topic to research. In some cases it is not an issue of performance (we haven't hit any issue yet), but of efficiency. Normal shards are replicated up to 20 times, and for certain usages that may be a waste (e.g. with some x1 services are ok being replicated just 3-5 times, like notifications, which are very heavy on writes).

@hoo, I think @Manuel got a bit alarmed because he may start to think you are requesting right now infrastructure, as you added the DBA tag (which normally we just use for actionable tickets/requests). I think if we move it to DBA (blocked external column) or Wikimedia-Rdbms it may be clearer that you only need feedback at some point and have it on the radar, but no immediate server actionables are needed yet.

We all agreed that this is something worth looking into, but there are various aspects that need investigation, some from the Wikidata team, some probably from the DBAs. I'll update the task description to reflect that.